In the conventional mobile communications system, the radio network controller RNC is configured to determines the transmission rate of uplink user data, by taking into consideration hardware resources for reception (hereinafter referred to as “hardware resources”) of the radio base station NodeB, uplink radio resources (an amount of uplink interference), transmission power of the mobile station UE, transmission process performance of the mobile station UE transmission rate required by a higher application, and the like; and to inform the mobile station UE and the radio base station NodeB of the determined transmission rate of the uplink user data as a Layer 3 (Radio Resource Control Layer) massage, when establishing a dedicated physical channel between a mobile station UE and a radio base station NodeB,
In this respect, the radio network controller RNC is an apparatus which provided in the higher position than the radio base station NodeB, and to control the radio base station NodeB and the mobile station UE.
Traffic occurs in a burst manner more often in data communications than in voice communications and TV communications. If possible, it is desirable that a transmission rate of uplink user data be changed at a high speed in data communications.
In the conventional mobile communications system however there is a problem that it is hard to control change of transmission rate of uplink user data at a high speed (for example, at a speed of approximately 1 microsecond to 100 microseconds), because the radio network controller RNC usually controls many radio base stations NodeB jointly, and it is assumed that process loads and process delays in the radio network controller RNC are increased.
In the mobile communications system, there is another problem that implementation costs of the apparatus and operating costs of the network run high, even though the change of transmission rate of uplink user data can be controlled at a high speed.
For these reasons, a usual practice of the conventional mobile communications system is to control the change of transmission rate of uplink user data at a speed of the order of several hundred microseconds to several seconds.
As a result, in the case where the conventional mobile communications system carries out data transmission in a burst manner, as shown in FIG. 2(a), it transmits data with accepting a low speed transmission, long transmission delays and low transmission efficiency, as shown in FIG. 2(b), or it transmits data with securing radio resources for high-speed transmission and accepting that radio band resources of available time and hardware resources of the radio base station NodeB are wasted, as shown in FIG. 2(c).
Note that, in FIG. 2, the axis of ordinates is denominated as both uplink radio resources and hardware resources.
In the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization groups for the third generation mobile communications system, high-speed uplink radio resource control methods in Layer 1 and Media Access Control (MAC) sublayer (Layer 2) between a radio base station NodeB and a mobile station UE have been examined, for the purpose of effectively using uplink radio resources. Hereinafter, the examination and functions examined there will be collectively referred to as “Enhanced Uplink (EUL)”.
In this respect, the uplink radio resource control methods which have been under examination within the “Enhanced Uplink” are roughly classified into the following three categories.
As a first uplink radio resource control method, “Time & Rate Control” is known.
As shown in FIGS. 3(a) and 3(b), in the “Time & Rate Control”, at a predetermined timing, a radio base station NodeB is configured to determine a mobile station UE which is allowed to transmit uplink user data to the radio base station NodeB and a transmission rate of the uplink user data; and to notify a mobile station ID for identifying the determined mobile station UE and the determined transmission rate of the uplink user data (or a maximum allowable transmission rate of the uplink user data).
And, in the “Time & Rate Control”, the mobile station UE is configured to transmit the uplink user data to the radio base station NodeB, at the predetermined timing and at the determined transmission rate of the uplink user data (or at a transmission rate within a range of the maximum allowable transmission rate of the uplink user data).
Otherwise, at a predetermined timing, the radio base station NodeB is configured to determine a mobile station UE which is allowed to transmit the uplink user data to the radio base station NodeB; to determine a transmission power of the uplink user data (or a transmission power ratio of an enhanced dedicated physical data channel (E-DPDCH) to a dedicated physical control channel (DPCCH) (hereinafter referred to as a “transmission power ratio”)), instead of determining the transmission rate of the uplink user data; and to notify a mobile station ID for identifying the determined mobile station UE and the determined transmission power of the uplink user data (or the determined transmission power ratio).
And, the mobile station UE is configured to determine the transmission rate of the uplink user data based on the notified transmission power of the uplink user data (or the notified transmission power ratio); and to transmit the uplink user data to the radio base station NodeB, at the predetermined timing, and at the determined transmission rate of the uplink user data.
As a second uplink radio resource control methods, “Rate Control” is known.
As shown in FIGS. 4(a) and 4(b), in the “Rate Control”, when there are uplink user data to be transmitted in a mobile station UE, the mobile station UE is configured to transmit the uplink user data to a radio base station NodeB.
In this respect, the radio base station NodeB is configured to determine a maximum allowable transmission rate, a maximum allowable transmission power or a maximum allowable transmission power ratio of the uplink user data, per one or more transmission time intervals (TTIs) of uplink user data, and to inform the mobile station UE of the determined one.
In this case, the radio base station NodeB is usually configured to inform the mobile station UE of a relative value to the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio (for example, a binary value representing UP command/Down command) at the present timing.
It should be noted that, in this case, the radio base station NodeB may be configured to assign a specific maximum allowable transmission rate, a specific maximum allowable transmission power or a specific maximum allowable transmission power ratio to each of mobile stations UE, or to assign a single maximum allowable transmission rate, a single maximum allowable transmission power or a single maximum allowable transmission power ratio to the entire cell.
Alternately, the radio base station NodeB may be configured to choose arbitrarily whether to assign a specific maximum allowable transmission rate, a specific maximum allowable transmission power or a specific maximum allowable transmission power ratio to each mobile station UE, or assign a single maximum allowable transmission rate, a single maximum allowable transmission power or a single maximum allowable transmission power ratio to the entire cell.
Note that a coefficient used for calculating the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio may be used instead of the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio.
As a third uplink radio resource control methods, “Autonomous Transmission” is known.
In the “Autonomous Transmission”, when there are uplink user data to be transmitted in a mobile station UE, the mobile station UE is configured to transmit the uplink user data to a radio base station NodeB whenever the mobile station UE has the uplink user data, whereas a maximum allowable transmission rate of the uplink user data is determined by the mobile communications system.
As described above, in the “Time & Rate Control” and the “Rate Control”, Layer 1 or MAC sublayer, which is provided to the radio base station NodeB, can control a transmission rate of the uplink user data at a high speed, so as to use uplink radio resources effectively, and to improve throughputs in the cell.
In the conventional “Time & Rate Control” however, the radio base station NodeB has to grasp whether or not each mobile station UE has uplink user data to be transmitted, what amount of uplink user data each mobile station UE needs to transmit, and the like. For this reason, periodically or whenever a predetermined event occurs, each mobile station UE is required to send such information to the radio base station NodeB via uplink control data.
By use of such information, the radio base station NodeB needs to assign adequate hardware resources for reception of uplink user data. For this reason, the radio base station NodeB needs to be provided with a control process for such an assignment. Therefore, there is a problem of making hardware configuration or software configuration of the radio base station NodeB more complicated, or a problem of prolonging a time needed to process the reception of the uplink user data.
Furthermore, in the conventional “Time & Rate Control”, every mobile station UE located in the same cell is configured to transmit its uplink control data to the radio base station NodeB Therefore, there is a problem that the uplink channel capacity runs short.
Moreover, in the conventional “Time & Rate Control”, the radio base station NodeB needs to transmit downlink control data for assigning uplink radio resources to each of the mobile stations UE existing in the same cell. Therefore, there is a problem that the downlink channel capacity runs short as well.
In addition, in the conventional “Time & Rate Control”, there is a problem that, when a reception error occurs in downlink control data, uplink radio resources which have been used to transmit uplink control data comes in vein.
Furthermore, in the conventional “Rate Control”, a signal for controlling the transmission rate of uplink user data needs to be transmitted via the downlink. Therefore, there is a problem that the downlink channel capacity runs short.
To ease these problems, examinations have been made for a method of controlling the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio of uplink user data, which can be realized by use of UP command/Down command (a one-bit command). However, there is a problem that an disagreement between a transmission rate of uplink user data recognized by the radio base station NodeB and a transmission rate of the uplink user data recognized by the mobile station UE occurs, and, in some cases, the radio base station NodeB fails to receive uplink user data transmitted by the mobile station UE, or a transmission rate of uplink user data which has been assigned by the radio base station NodeB is not implemented and the use of the u-link radio resources for the transmission comes in vain, in the case where a bit error occurs in such a command.
Furthermore, in the conventional “Rate Control”, there is a problem that, if the radio base station NodeB controls the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio of uplink user data by transmitting a single UP command/Down command to all the mobile stations UE throughout the cell, this control hinders the assignment of the uplink radio resources among the mobile stations UE from being equal.
Suppose that, as shown in FIG. 5, there are a mobile station UE#1 which has started to transmit data first, and a mobile station UE#2 has started to transmit data later, in a certain cell. When uplink radio resources are still available in the cell, the radio base station NodeB transmits an UP command. For this reason, uplink radio resources assigned to each of the mobile stations UE#1 and UE#2 become large in amount with lapse of time Finally, all the uplink radio resources in the cell are used up.
In this occasion, because the mobile station UE#2 starts to transmit data later than the mobile station UE#1 does, the mobile station UE#2 receives a smaller number of UP commands from the radio base station NodeB than the mobile station UE#1 does, and the uplink radio resources assigned to the mobile station UE#2 is smaller in number than those assigned to the mobile station U#1. As a result, there is a problem that the assignment of uplink radio resources is not equal between the mobile stations.
Furthermore, in the conventional “Rate Control”, when a method of informing the entire cell of the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio of uplink user data (or the coefficients used for calculating the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio of uplink user data) is used (hereinafter, referred to as a “cell common rate control method”), there is a problem as follows. Even if actual traffic is small in amount, in a case where mobile stations UE connected to the radio base station NodeB are large in number a larger amount of hardware resources need to be made available in the radio base station NodeB, and this increases the reception buffer capacity of the radio base station NodeB. As a result, this increases equipment costs.
In other words, since all the mobile stations UE connected to the cell use the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio (or the coefficients for calculating the maximum allowable transmission rate, the maximum allowable transmission power or the maximum allowable transmission power ratio) which is common among the mobile stations UE, in the cell common rate control method, there is a problem that the radio base station NodeB needs to make the same amount of hardware resources available for a mobile station UE with a smaller amount of traffic as for a mobile station UE with a larger amount of traffic.
Moreover, the conventional “Autonomous Transmission” has been examined as its combination with the “Time & Rate Control” or as its combination with “Rate Control”. The conventional “Autonomous Transmission” is not capable of controlling a maximum allowable transmission rate of uplink user data by use of Layer 1 or MAC sublayer. For this reason, in the conventional “Autonomous Transmission”, a transmission rate of uplink user data needs to be controlled by use of Layer 3, which is provided to the radio network controller RNC, as in the case of the prior art. As a result, it is not expected that the conventional “Autonomous Transmission” improves the effective use of uplink radio resources by itself.